A device has been proposed which estimates traffic conditions around a host vehicle on the basis of information acquired by, for example, inter-vehicle communication with other vehicles and performs driving assistance corresponding to the estimation result. For example, Japanese Unexamined Patent Application Publication No. 2006-185136 discloses a driving assistance device that estimates the number of other vehicles which cannot perform communication between the host vehicle and another vehicle which travels in front of the host vehicle and can perform inter-vehicle communication on the basis of the distance between another vehicle and the host vehicle. In the driving assistance device, when the number of other vehicles which cannot perform inter-vehicle communication is estimated from the inter-vehicle distance, the interval at which there is a communication-incapable vehicle is calculated using various maps corresponding to an inter-vehicle time, a traveling time, and a traveling region on the basis of the speed of another vehicle acquired by inter-vehicle communication. In this manner, estimation accuracy is improved.